1. Field of the Invention
The present invention relates to a rotational position sensor for detecting the rotational position of a rotating axis of a throttle valve used in an internal combustion engine, for example, and more particularly to a non-contact rotational position sensor.
The present invention also relates to a throttle valve assembly including the non-contact rotational position sensor.
2. Description of the Related Art
Conventional rotational position sensors of the above-mentioned type are disclosed in Japanese Patent Nos. 2842482 and 2920179 and U.S. Pat. Nos. 5,528,139, 5,789,917 and 6,137,288.
Those prior-art sensors are based on the fact that, taking the permanent magnet side as a rotor, the circumferential magnetic flux density in a stator is linearly distributed relative to the rotating direction of the rotor. To avoid as perfect as possible a magnetic field distribution in the stator from being affected by the rotational position of the rotor to which the magnet is attached, confronting surfaces of the rotor and the stator are shaped such that their lengths are even in a direction perpendicular to the rotating direction of the rotor.
Because of such a limitation imposed on shapes of the confronting surfaces of the rotor and the stator, the conventional rotational position sensors have a problem that flexibility in design is low when the sensors are designed to be adapted for target equipment to which the sensors are attached.